Kirika Yuumura is an assassin who worked with Mireille Bouquet under the codename Noir. Much about her past is mysterious, even to her; she experienced severe retrograde amnesia almost immediately prior to meeting Mireille, and since then has recovered only fragmentary memories. Despite her young age, memory loss, and a certain naiveté, Kirika possessed the skills of a superbly-trained killer. Her preferred weapon was a Beretta M1934 pistol, although she was also an expert at killing people with whatever was at hand.

Kirika's hair is black(short) and her eyes are red/brown. Her usual outfit is comprised of a white jacket, light green shirt, blue skirt and ruby shoes. In the episode "Daily Bread", she wears overalls with the Wu-Tang Clan logo on them.
During the Noir ritual she wears a very short golden dress identical to Chloe’s.

Kirika bears a strong resemblance to Ein from Requiem for Phantom in both appearance and personality.

Kirika's real name, parents, and place of origin remain total unknowns. At a very young age, she was chosen by the secret society Les Soldats as a candidate for Noir, a duo of elite female assassins who would represent one of the organization's most powerful instruments of control. She began her training almost immediately and achieved her first two kills at the age of eight, when she took the lives of Laurent and Odette Bouquet. Odette's final words were a request that Kirika take care of her daughter Mireille, also a Noir candidate, through the difficult trials the candidates would face.

At the age of fifteen, Kirika was brought to Japan under a false identity as a normal student. An unknown event caused her to experience near-total amnesia, and thereafter, she could recall nothing of her life with the Soldats - although her training and her instincts remained untouched. She was left with just enough clues to contact Mireille Bouquet, and convince her to search for answers with Kirika. Mireille only agreed because she believed the reason for her parents' murders was part of the same puzzle.

The two gradually uncovered the existence of Les Soldats, their own status as candidates for Noir, and finally, their connection to one another. Mireille, despite having found her parents' murderer, could not bring herself to kill her partner. After seeing their quest to its conclusion, they returned to Paris to live not under the thumb of the Soldats, but as they saw fit.